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P.H. Ltd Spinthariscope, 1970?
The Spinthariscope was
invented back in 1903, by William Crookes and for most of the past 100
years they have been regarded as interesting novelties and educational
toys. This one, which I believe dates from the late 60’s was designed for use
in schools, which explains its rather battered appearance. The reason you don’t see
them very often is because inside there’s a speck of radioactive material,
0.02 micrograms of Radium to be precise. It all sounds a bit scary but
the fact is, the Radium source is miniscule, less radioactive than the sensors in most household
smoke detectors, and a magnitude less than old watches and clocks with luminous
hands but anything labelled as radioactive these days worries a lot of
people… See my anythingradioactive site
for a basic guide to radioactivity and – shameless plug – lots of cheap Geiger
counters and nuclear novelties. The Radium source shoots out alpha particles, and if you know anything about radioactivity you’ll know these are the weakest sort, barely able to penetrate a sheet of paper (though you certainly wouldn't want a lof of them inside your body...), but the point is none can escape from the cannister.
Inside the tiny piece of Radium
is mounted on a small spike in the middle and beneath it there’s a coating of a
chemical that almost certainly includes Zinc Sulphide. This has a very
interesting property. When it is struck by an alpha particle it emits a brief
flash of light, and this is what you see when you look through the eyepiece. You have to use it in total darkness, and you need to allow at least five minutes to let your eyes adjust, but it’s worth the wait and you’ll see hundreds of flashes each minute as atoms disintegrate and smash into each other. What Happened to ItSpintariscopes have rather gone out of fashion thanks largely to misinformed attitudes towards radioactivity and the inevitable health and safety concerns. Nevertheless, at least one company in the US is still making them, but does not export them outside the US (even though you would need tens of thousands of them to make a small 'dirty' bomb).
This one isn’t that special, it turned up in a box of lab equipment bought at a
boot sale a couple of years ago and the whole lot only cost me £5.00.
However, good ones are most defintiely collector's items. Original ornate wood and brass Crookes ‘pattern’ Spinthariscopes,
dating from the 1920s and 30s, are worth a small fortune and I have seen them
selling on ebay to collectors for several hundred pounds. GIZMO GUIDE
First seen: 1903 Original
Price
£? Value Today? £25 Features:
Eyepiece with magnifying lens, 0.02ug Radium source Power req.
n/a
Weight: 0.18kg Dimensions: 68 x 60mm Made in: England Hen’s Teeth (10 rarest): 8
Taylor Instruments Barograph, 1975
The top of the bellows is
connected by a lever mechanism to a simple pen nib and ink reservoir, on the
end of the arm, and this draws a continuous line on a strip of chart paper,
attached to a drum that rotates once a week. The drum, in this case, is driven
by a battery powered clock movement in the base, which makes it a bit unusual. The
drums on most ‘classic’ barographs are usually driven by clockwork movements,
which is probably why ones like this are eschewed by serious collectors, and
can still be found relatively cheaply. It’s small size and the
fairly plain, functional design and Perspex dust cover makes me think this particular model was made
for schools and libraries and so on, rather than for ornamental, scientific or
domestic use, even so it’s a really interesting object to have around, and
functional too. The pen trace gives you a real-time indication of the weather,
as it is now, and as it has been, and with a little practice you can spot
trends and take a fairly good guess at what the weather will be. What Happened to it? Barographs of this type are
still being made and good ones cost hundreds, if not thousands of pounds, and
antique ones – especially fancy models from top name makers – cost a small
fortune. Nowadays, though, anyone seriously interested in recording air
pressure will use an electronic instrument or one kind or another. Barographs can be quite
expensive to run. Blank recording charts are quite difficult to find, and when
you do they can be silly prices, so I make my own. I found one the right size
and scanned it, erased the ink trace with PaintShop Pro and print them out as
needed. To prevent the ink soaking in I spray them with a fixative spray.
Special barograph ink is also very expensive, so I make my own. Ordinary
‘Quink’ type pen ink dries out in a few days, so to stop that happening just
mix it with glycerine, a 50/50 mix works just fine. I bought this one from good
old ebay a few years ago for £30, the only trouble was the seller was Canadian,
so it cost me another £30 to have it shipped over (and careful packaging is
essential) but it was money well spent and I have seen them selling for two or
three times as much, through the occasional bargain still slips through,
especially when the seller doesn’t know what it is and it ends up in the wrong
category, or can’t spell the word barograph…. GIZMO GUIDE
First seen: 1930 Original
Price
£? Value Today? £100 Features:
7-day movement, continuous barometric
pressure recording, Perspex dust cover Weight: 1kg Dimensions: 198 x 111 x 135mm Made in: USA Hen’s Teeth (10 rarest): 4 AVO Model 8 Multimeter 1965
By current standards the AVO 8 is fairly basic; all it does is measure AC and DC voltage and current and electrical resistance. You can buy a pocket test meter in Maplin for under a tenner that does all that, and quite a bit more besides, and probably more accurately -- but I absolutely guarantee it will not be still working in 40 or 50 years time. AVOs even older than that are still in daily use. What an AVO 8 and analogue meters lack in fancy features they more than make up for with the extra information they provide about the circuits they are being used to test. It takes a while to learn and understand the behaviour or a wiggling moving coil meter but it’ll tell you more than a bunch of digits ever will. However, what really sets the AVO 8 apart from almost every other test meter is its rugged construction. In short it’s built like a brick outhouse and can take a ridiculous amount of physical punishment, and if you do abuse it electrically the fast mechanical cut-out usually saves the day. There’s not really much to say about the technology, it’s simple and it works, the only points of interest to those unfamiliar with mechanical test meters are things like the curved mirror on the meter scale. This is used to improve accuracy; it’s elegantly simple, when reading the dial you position your eyes so that you can’t see the reflection of the needle, at which point you know you are looking directly down on the scale. One less welcome feature is the really unusual 15 volt battery it uses to power the resistance measurement circuit. Fortunately they last for ages, and they are still available, though it’s a constant source of worry that one day they’ll stop making them What Happened to it? The Model 8 was introduced in the early 1950s and this one, one of two that I own, is a fairly early example because it has a (notoriously inaccurate) decibel range. Legend has it that it was designed to meet military specifications but the manufactures decided it was so good it was developed for the civilian market. As a matter of interest the Model 8 is still being made and costs around £600, though AVO has long since moved on to more hi-tech products and sadly most of it’s model range is now manufactured overseas. I can’t honestly remember what I paid for my two AVO 8s, one I’ve had for at least 25 years, the other I found at a car boot sale ten years ago so it probably only cost £5 or so. They are not especially collectible so you can expect to find bargains but for a generation of old hands that grew up with them they are still very useable test instruments and their worth goes way beyond mere monetary consideration. GIZMO GUIDE
First seen: 1951 Original
Price
£30 Value Today? £10 Features:
28 ranges: DC Current 50uA - 10A, DC Voltage 2.5 –2500 volts, AC
Current 100mA - 10A, 0 – 20M Ohms, insulation resistant ace up to 200M (with
external 150 volt supply) sensitivity 20,000 Ohms/volt, 1% accuracy Weight: 2.75kg Dimensions: 195 x 170 x 115mm Made in: UK Hen’s Teeth (10 rarest): 6 AVO Multiminor, 1966 (manual)
The Multiminor was designed
for portability and use in the field or up ladders so it’s relatively small and
light, and very easy to use. There’s only two controls, the large range/mode
switch and the small ohms ‘zero’ preset, which you twiddle to compensate for
the aging effect of the single AA battery, used to measure resistance. There’s
also a meter zero adjustment, though this would normally only be set if the
meter had suffered a severe shock, or set to the wrong range, and the needle
had wrapped it self against the end-stop… This model range has also
been around for a long time and I have found references to Multiminors dating
back to the 1930s. This particular one is almost certainly from the mid to late
1960s, judging by the materials and the design of the leather carry case. The
top panel and switch are all made from black Bakelite and the lower part is a
hammer-finished steel pressing; earlier models were all Bakelite. The leads are not original,
and like most well-used AVOs they are probably the third or fourth set, earlier ones being lost, stolen, destroyed or the insulation burned by a carelessly placed
soldering iron. What Happened to It? Analogue test meters are
now very rare, having been largely replaced by digital instruments,
nevertheless, AVOs and their ilk will continue to find favour with engineers,
especially those from the old school, who appreciate the extra information they
can give, and their inherent reliability. Analogue AVO meters were produced in fairly
large numbers, so they’re not especially rare, and they’re virtually indestructible,
so you’ll regularly find good examples selling on ebay, often for a fraction of
their real worth (or original cost). A good example of a practical and genuinely
useful collectible, but probably not much of an investment. GIZMO GUIDE
First seen: c1966 Original
Price
£50 - 150 Value Today? £10 Features:
Measuring ranges DC volts: 2.5, 10, 25, 100, 250, 1000; AC volts: 10, 25, 100, 250, 1000 V; Current: 0.1, 1, 10, 100, 1000 mA; Resistance:
x1, x100k ohms Weight: 0.5kg Dimensions: 143 x 92 x 35 mm Made in: Archcliffe Road, Dover, Kent, England Hen’s Teeth (10 rarest): 4 TTC C1001 Multimeter, 1971
There was a healthy magazine market too, with titles like Practical Wireless, Radio Constructor, Practical Electronics. Elektor and Electronics Today International (ETI, who gave me my first job in journalism). Each month these magazines published detailed plans for impossibly complicated electronic gadgets, most of which never worked, and the must-have accessory was a Multimeter, so you could find out what went wrong with it. Incidentally, after working for various electronic constructor magazines over the years I can tell you that at least half the things we published never worked and one of my first jobs was to put together the corrections page each month. Also, my sincere apologies for anyone who received shocks from the many dodgy mains-powered projects we occasionally and most unwisely published… Anyway, this particular multimeter dates back to the early 70’s and was ideal for simple projects, being able to measure AC and DC voltages, small currents and resistance. It was reasonably accurate and a pocket-money alternative to serious multimeters like the magnificent AVO models used by serious teccies. This one is based around a large angled moving coil meter, housed in a sturdy bakelite case and it came with a leather carry case and pair of tests leads.
What happened to it? Most test meters had gone digital by the late 70’s and very accurate they were too, giving precise readings of volts, ohms, amps and much more besides to several decimal places. However, call me an old stick in the mud but I still prefer to watch a flickering needle. I genuinely believe it tells you more about what’s happening in an electrical or electronic circuit than a set of digits. Changes in current or voltage, for example, are much easier to see when represented by a moving needle. It’s also easier to judge the performance and condition of a capacitor by measuring its resistance, and watching the charge quickly rise and slowly fall. Most moving coil multimeters of this era were built like brick outhouses and they didn’t reven need a battery for measuring volts and amps (the battery was used for checking resistance).
Old test meters pop up now and again in junk markets and car boot sales. However, it is unlikely that cheap little ones like this will ever become seriously collectable but big old AVO meters are definitely worth having; they are superbly well built and to anyone who has used one, a thing of beauty and precision.
GIZMO GUIDE
First seen: 1971 Original
Price £8.95 Value Today? £2 - £5 Features:
Moving coil meter,
DC volts 5 – 500/2.5k, AC volts 10 – 1000, DC current 0-5uA/0-250mA, DC
Resistance 0-infinity 2 x ranges Power req. 1 x AA Weight: 400g Dimensions: 115 x 85 x 28 (very approx) Made in: Japan Rarity: 6 (1 = common, 10 = Hen's teeth)
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This rather disreputable
looking object is definitely not something you see every day. It’s a
Spinthariscope, and the idea is you look through the eyepiece and watch atoms
splitting, really!
At least, I’m fairly sure
it’s made by Taylor Instruments, and the date is a bit of a guess as well.
There are no manufacturer’s marks or dates anywhere but it looks a lot like
barographs made by the company, of that era. In case you’re wondering what a
barograph is, it’s an instrument for recording changes in air pressure, and if
you’re familiar with aneroid barometers -- the sort you hang on the wall, with
a round dial, marked ‘stormy’ and ‘change’ – then you may recognise part of the
mechanism inside the case. The stack of round cylinders on the right is a type
of bellows, all the air has been sucked out so when the atmospheric air
pressure changes they expand or contract.
In my opinion you are now looking at one of the finest
electrical test and measuring instruments ever built and until a few years ago,
if you ever needed to have a piece of electronic equipment repaired there’s a
very fair chance an AVO meter, and quite probably a Model 8, had something to
do with it. 
Anyone who has worked in
the electrical or electronics industry will be familiar with the name AVO.
British made AVO (short for Amps, Volts and Ohms) test meters and instruments
are justly famous for their accuracy, reliability and above all, the kind of
rugged construction that means they can take a great deal of punishment. The
design of AVO meters changes little over the years and the classic Model 8
analogue multimeter, which I was using back in the 1970s is still being made,
and nowadays costs the thick end of £600!
Back in the 60’s and 70s there was huge amount of dabbling
going on. Boys of all ages (and it was very much a boy thing), especially nerdy
ones, were into electronics in a big way. For a short while electronic
construction kits were all the rage but for the hardcore enthusiast it had to
be DIY all the way, which meant learning which end of a soldering iron to hold,
and buying your transistors, resistors and capacitors from the dozens of
companies that sprung up all over the place.